Prosthetic bone implantation and joint replacement is well known in the art. Proper alignment of the implanted prosthesis is critical to the long term success of the implantation, and improper positioning can cause instability, impingement and increased wear. Misalignment of a prosthesis can also lead to soft tissue imbalance, joint dislocation, compromised range of motion and increased pain to the patient.
Having been in use since the mid-20th century, a conventional method of aligning a prosthesis relies on a statistical range of alignment values based on statistical anatomic studies. Using the statistical range as a guide, the surgeon visually estimates the proper angle to implant the prosthesis. As an example, for implantation of a humeral prosthesis, the statistical range for the retroversion angle is about 25 degrees to about 35 degrees based on anatomical studies. However, the retroversion angle can vary up to about 82 degrees and may be influenced by such factors as age, sex, race, and handedness. Similar variability exists for other prosthetic implants and alignment variables in other joints such as the femur for hip arthroplasty procedures.
Some researchers have experimented with computer-aided navigation systems. However, the utility of computer-aided navigation systems has not been fully explored, and the technique is expected to increase surgical times, particularly with medical professionals new to such technology. Preoperative CT scans can also be used to determine the proper alignment, but use of this technique results in increased radiation exposure to the patient, which is undesirable. Some mechanical devices to align prosthetic implants exist, but these devices rely on the statistical average range of alignment values based on the anatomical studies and do not account for the full range of variability. These devices do not re-create the native alignment and, therefore, often result in misalignment leading to the aforementioned consequences.